The present invention, in some embodiments thereof, relates to nanotags for authentication and, more particularly, but not exclusively, to large scale production of such nanotags.
Product theft and counterfeiting are steadily growing around the world. As stated in the Netnames report, Counting the cost of counterfeiting, 2016, “In an environment where counterfeiting is as profitable as illegal drugs, but remains far less risky for criminals, we are seeing explosive growth. Expanding by over 15% every year, counterfeiting now costs more than 2% of total global economic output, or around $1.8 trillion per year”
In light of the scale of the problem, a simple, cost effective and hard to forge authentication tag is thus required. In recent decades, many solutions have been proposed to address the problem of product theft and counterfeiting. A tag which is easy to generate by the official distributor, easily read by the end user and hard to copy is a basic requirement.
As the race between manufacturers and forgers ever escalates, the ruling paradigm has traditionally been to periodically increase the level of complexity of authentication tags, in an effort to keep ahead of counterfeiters. State-of-the-art optical tags feature a primary layer of security, evident to forgers, and often replicable, and a secondary layer of security, typically involving complex interrogation methods, raising the bar for counterfeiters, and relying on trade secrets for their composition or fabrication methods. A simple, low-cost, authentication tag, easily interrogated for its encoded message, and also for its secondary security layer, is of great need and has yet to be demonstrated.
Current solutions ranging from complicated bio-markers to simple invisible inks have been suggested. Known solutions include a variety of techniques such as holograms, RFID, special inks, watermarks, and bio-markers. Some of these methods employ low resolution structures which can be relatively easily replicated and counterfeited. Others, based on special materials, require complex facilities for the authentication procedure. RFID chips, in particular, can be remotely interrogated without coming into contact with the product and the chip can be replicated. Their size inhibits their use for many applications. The most secure authentication approach employed today is based on bio-markers (e.g. DNA strands, etc.) which are almost impossible to counterfeit. However, the authentication process of these markers is complex and necessitates a forensic lab, thus rendering it impractical for many applications, especially where hand-held interrogation is required. Other optical anti-counterfeit tags can be roughly divided into the following categories: taggants forming special images, with distinct appearances under different illumination conditions; barcode taggants primarily displaying encoded information, and supporting a secondary security layer; and intrinsically random patterns, such as dropcast nanomaterials, which are unique and unclonable. The latter offers the simplest fabrication and a very high level of security, being a high resolution large area distribution. However, it involves a comprehensive interrogation, compiling a database per tag, which is then passed on as a secret to all other interrogating entities.
Thus there is an inherent tradeoff between the tag security level and its ease of fabrication. While bio-markers offer an extremely high security solution, they are very hard to generate and be verified by the end user. A relatively good compromise between easy handling and difficulty to forge can be achieved using holograms generated using metallic nano-structures. Such tags are based on metallic nano-elements, which generate a desired hologram when illuminated. They are easy to read but hard to copy.
Such a nano-tag may provide an authentication tag to prevent counterfeiting. Almost every brand in the world is subject to replication and theft. An inexpensive tag which may ensure the authenticity of the brand may be a very desirable product.
The technology is based on the following scheme. An array of nano metallic structures is illuminated with a light beam and results in a reflected hologram. If the reflected hologram matches the expected pattern, then it may be inferred that the specific product is authentic. The detection scheme is based on the phase difference generated by each element of the metallic nano-structures. The complete phase imposed on the impinging beam result in the reflected hologram. The metallic elements in the array are of nanometer scale what makes them hard to forge.
When illuminated, the nano-structures reflect a unique pattern which can be verified using a simple detector. While the detection scheme is straightforward, the fabrication of these structures can be complicated due to their nanometer scale. The most common way for generating nanostructures is by using electron beam lithography (EBL). Although EBL is very accurate, it is a serial fabrication process, meaning each element has to be written separately, as opposed to parallel techniques which can generate the whole pattern in one step, hence, relatively slow and expensive rendering it less compatible for commercialization.
In order to overcome these drawbacks, a parallel method for generating nano structures designated as nano imprint lithography (NIL) designated sometimes as soft lithography when using a soft material for the mold, has been demonstrated.
The NIL technique is illustrated in FIG. 1A-FIG. 1D and may comprise four steps for generating metal structures:
A) Fabrication of a master template (Using EBL for example).
B) Generation of a negative instance—mold—of the master by molding a suitable material onto the master.
C) Generation of a positive replica of the master by imprinting the mold onto a suitable material.
D) Deposition of metal on top of the replicated pattern to achieve metallic nano structures.
Thus, although the master is expensive and complicate to generate, it is now much faster and simpler to generate multiple replicas thereof. Note that step C in the process requires delicate alignment between the mold and the target substrate (especially when using hard molds) and equal force distribution which usually requires large and expensive machinery, particularly for mass production.
NIL thus has the disadvantage of requiring large and expensive machine, particularly for mass production.
Additional background art includes US 2014/0175171, System and Method for nano-imprinting Feb. 25, 2014, U.S. Pat. Nos. 8,678,284 and 9,104,948.